Currently, there are various kinds of satellite navigation devices that perform positioning and generation of a reference signal such as 1PPS by using the GNSS (Global Navigation Satellite System). In such satellite navigation devices, the positioning and the generation of the reference signal are performed based on navigation signals from a plurality of navigation satellites. Here, since the GNSS includes a plurality of systems controlled by different administrators, a case of the GPS (Global Positioning System) is described below as an example.
In the GPS, an L1 wave and an L2 wave having frequencies different from each other are carrier waves to which a pseudo-noise code and a navigation message are overlaid. Accordingly, each of the GPS satellites generates a GPS signal. Hereinafter, the GPS signal using the L1 wave is referred to as an L1 signal and the GPS signal using the L2 wave is referred to as an L2 signal. In each of the GPS satellites, the L1 signal in synchronization with the L2 signal goes on the air. The satellite navigation device receives the synchronized signal.
The satellite navigation device calculates a pseudo range P for each GPS satellite based on the pseudo-noise code upon receiving the GPS signal and estimates a position and a receiver time error based on the pseudo range P. In this estimate operation, precision of the pseudo range affects precision of a result of, for example, the positioning. However, since the pseudo range has a margin of error, correction processing for correcting the pseudo range becomes essential in order to achieve, for example, positioning with high precision. Currently, various kinds of correction processing for correcting the pseudo range are proposed, for example a method of smoothing the pseudo range with a carrier phase and a method of correcting the pseudo range with the ionosphere delay.
For example, in Patent Document 1, after an ionosphere delay amount of the L1 signal is calculated based on the pseudo range of the L1 signal and the pseudo range of the L2 signal to smoothen the ionosphere delay amount, the smoothened amount is differentiated from the pseudo range of the L1 signal. Accordingly, the ionosphere delay correction is performed.
In Patent Document 2, an ionosphere-free code pseudo range is calculated based on the pseudo range of the L1 signal and the pseudo range of the L2 signal, and an ionosphere-free carrier phase is calculated based on a carrier phase of the L1 signal and a carrier phase of the L2 signal. Then, the ionosphere-free carrier phase is differentiated from the ionosphere-free code pseudo range to smoothen the resulting value for the correction.
In addition to the above, there is another method that performs typical carrier smoothing. In this case, the ionosphere delay amount after the carrier smoothing is differentiated from the pseudo range after the carrier smoothing, thereby achieving the ionosphere delay correction of the pseudo range.
Patent Document 1: JP2008-51567A
Patent Document 2: JP2007-278708A